Ellipsometric Analysis of Growth Process and Corrosion Resistance of Nb2 O 5 Films Formed by MOCVD

Abstract

The formation process of Nb~O~ films by metallorganic chemical vapor deposition using pentaethoxy niobium (PEN: Nb(OC~H~)~) as a vapor source and O~ as reactant gas has been analyzed by in situ ellipsometry at substrate temperatures of 200 to 500~ and at O~ flow rates of 0 to 2000 cm~/min. According to the changes in the refractive index and the growth rate of the films, the formation process can be divided into three stages, that is, the nucleation and coalescence, the homogeneous growth, and the surface roughness evolution stages. The refractive index and the growth rate of the films were found to depend on the substrate temperature and the O~ flow rate. The films deposited at 200 to 400~ had amorphous structures, and those deposited at 450 to 500~ contained a 8-Nb~O~ phase in an amorphous matrix. The corrosion resistance of the films in a buffered I-IF solution depended on both the deposition temperature and the O~ flow rate. The film deposited at 450~ in the absence of O~ showed the highest corrosion resistance against the solution.Thin Nb2Q films have been proposed for various applications such as dielectric layers in thin film capacitors, :'2 antireflection coatings for solar cells, 3 and optical waveguides, ~ because of the high dielectric constant (e = 11 to 1007 and high refractive index (2.2 to 2.6 at 546.1 nm)J Moreover, excellent chemical stability of Nb~O~ ~ suggests that this material can be used as corrosion resistant coatings. Several techniques including electron beam evaporation, ~ plasma oxidation, ~' halogen transport, ~ and chemical vapor deposition, ~ have been employed to produce Nh~O~ films. Among these techniques, metallorganic chemical vapor deposition (MOCVD) using the pyrolysis of metal alkoxides is attractive as a preparation method for corrosion resistant oxide coatings, because it offers the following advantages: (i) process simplicity, (it) lower processing temperatures to obtain high density films, (iii) good uniformity and step-coverage of films, and (iv) control of the stoichiometry. However, it is necessary to optimize process parameters to produce metallorganic chemical vapor deposition (MOCVD) oxide films with a good corrosion resistance. ~ It has been reported that the properties of Ta~O~, ~,~0 TiQ, n ZrO~, ~= and AI~O~ ~ films, which were formed by MOCVD using corresponding metal alkoxides, change with deposition time as well as with substrate temperature. It is therefore important to elucidate in situ the change in film properties during deposition under various conditions. The aim of this study is to analyze the growth process and corrosion characteristics of Nb~O~ films formed by MOCVD using pentaethoxy niobium (PEN: Nb(OC~H~)~) as a vapor source. In situ ellipsometry was employed for observing changes in the thickness and optical constants of the films * Electrochemical Society Active Member. during deposition. The dissolution rates of the films were also measured by el]ipsometry in a buffered HF solution. ExperimentalMOCVD apparatus.--Nb20~ films were deposited by MOCV...

Effect of post annealing treatment on electrochromic properties of spray deposited niobium oxide thin films

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Characterization of Niobium Oxide Films Prepared by Reactive DC Magnetron Sputtering

“…Niobium oxides find a variety of applications in modern technology in different components ranging from capacitors [1], to waveguides [2], oxygen sensors [3] and as corrosion resistant material [4]. Apart from this, niobium oxide films are used as high refractive index layers in optical interference filters [5] which consist of a multilayer stack of high and low refractive index materials.…”

Photoluminescence of amorphous niobium oxide films synthesized by solid-state reaction

“…It is an important component in mend -alloys improving corrosion resistance [5]. Importantly, niobium oxide is used as high refractive index layers in optical interference coatings [6].…”